In “open-flow microperfusion” (OFM), in order to capture the alterations or levels of biochemical entities at tissue level in vivo for instance blood glucose levels subcutaneously, a needle-like catheter may be inserted into tissue, for instance in adipose tissue, muscle tissue, or skin. Linear catheters with a single lumen and an exchange area can be used to establish flow-through path for perfusion fluid. Using a double-lumen catheter, a perfusion fluid is continuously infused through the inner lumen and withdrawn through the annular space between the inner cannula and the outer catheter tubing. Because of partial equilibration between the interstitial fluid and the perfusate, the perfusate is enriched by surrounding substances (or solutes, entities, molecules), such that the substances can be detected in the outflow. For instance, a glucose sensor outside the body can capture glucose from the aspirated fluid. The fluid in the outflow (sample, aspirated fluid) is not a dialysate resulting from a membrane process, but to keep the analogy between microdialysis and microperfusion the term “dialysate” herein may also mean microperfusion outflows fluids.
However, implantation of a cerebral catheter into a brain involves injuries of the brain. Particularly, cerebral OFM is rendered difficult when using conventional approaches.
When implanting a cerebral catheter, the so-called blood-brain barrier can be disturbed or even disabled by the injury of the brain being caused by the implantation. The intact blood-brain barrier provides for a separation of circulating blood and cerebral extracellular fluid in the central nervous system. Endothelial cells restrict the diffusion of microscopic objects (for instance bacteria) and large or hydrophilic molecules into the central nervous system, while allowing the diffusion of small hydrophobic molecules (O2, CO2, neuroactive drugs,).
As long as the blood-brain barrier remains disturbed or even disabled by the injury, no meaningful OFM or microdialysis measurement of transport over blood-brain barrier is possible. On the other hand, maintaining the implanted catheter in the brain until the blood-brain barrier has recovered is not possible as well, since this procedure may take several days so that cerebral tissue may grow into the catheter during this time. This renders cerebral catheter technology very difficult.
Although cerebral catheters are specifically delicate, different types of catheters suffer from problems arising from the risk of injury during implantation or removal.
WO 2002/056937 discloses a system for delivering substances or apparatus to an extravascular target site within the body of a human or veterinary patient, said system comprising a vessel wall penetrating catheter that comprises a catheter body that is insertable into the vasculature of the patient and a vessel wall penetrating member having a lumen extending longitudinally therethrough, said penetrating member being passable from the catheter body and through the wall of a blood vessel in which the catheter body is positioned, and a delivery catheter having a lumen extending longitudinally therethrough, said delivery catheter being advanceable through the lumen of the vessel wall penetrating member to an extravascular target site, said vessel wall penetrating member being retractable into the catheter body of the vessel wall penetrating catheter and the vessel wall penetrating catheter being removable from the patient's body such that the delivery catheter remains indwelling with the distal end of the delivery catheter located at the extravascular target site.
WO 2004/096314 discloses a catheter assembly for intracranial treatment of a patient, wherein the assembly comprises an outer catheter and an inner catheter. The outer catheter includes a proximal opening, at least one aperture, a lumen connecting the opening and the aperture, and at least one element. The inner catheter is adapted to be received within the lumen and includes a passageway and at least one port for transferring fluids between the inner catheter and a tissue region within the patient's brain. The assembly facilitates regular accurate placement of the drug delivery catheter at the tissue region without additional extended contact with the brain during insertion.
WO 2007/138590 discloses an implantable pump for pumping a drug in a patient's body. The pump includes a drug delivery chamber configured to be filled with the drug and a drug delivery catheter having a catheter lumen and a distal end, the drug delivery catheter in fluid communication with the drug delivery chamber and configured to deliver the drug to a delivery site. It also includes a pushing element coupled to the distal end of the catheter, and configured to push away from the catheter lumen fibrotic matter that has developed in response to the drug delivery catheter.
US 2006/235349 discloses cerebrospinal fluid shunts (implantable devices for diversion of excess fluid from the brain to other body cavities) used to treat hydrocephalus often malfunction. A common etiology of shunt malfunction is obstruction of the distal catheter tip by accumulating particulate matter such as fat or proteinaceous debris. The proposed implantable device maintains the patency of the cerebrospinal fluid shunt with mechanical energy which serves to “scrub” the catheter lumen of particulate debris. The device accomplishes this by housing a source of mechanical energy which is coupled to the external aspect of the catheter, itself traversing through a bore in the device. The energy source secondarily induces a waveform in the cerebrospinal fluid flowing through the catheter. The fluid waveform exerts shearing forces on the catheter wall and serves to disrupt the formation and accumulation of debris that potentially could occlude the shunt catheter, thereby maintaining patency of the shunt.
It is however a shortcoming that conventional approaches do not allow to safely prevent ingrowth of tissue into a catheter which may cause problems when the catheter or parts thereof are maneuvered within a physiological body.